The present invention relates to a bit map image processing apparatus having a hardware window function.
In recent bit map image processing apparatuses such as a bit map display apparatus, a display function called multiwindow display is needed to display a plurality of data on a single display screen. As a means for performing window display, (1) a software window in accordance with a bitblot scheme (bit block transfer scheme); and (2) a hardware window in accordance with display address control are conventionally known as described in NIKKEI ELECTRONICS, 1986. 5. 19 (no. 395. pp. 221-250). With software method (1), when the window size is increased, the transfer time is prolonged, as described in the above literature. In addition, the response speed is lowered and priority setting is complex when windows overlap.
In contrast to this, with hardware method (2), in the case of i82786 (display control LSI available from Intel Corp., U.S.A.) described in the above literature, if the number of windows is increased, updating of the contents of a memory such as a descriptor becomes complex when a window is to be moved, a display address is to be changed, or the priority is to be changed. Also, the number of memory access times performed by i82786 is increased, resulting in degradation in performance of the processor. In i82786, when an image 2-port memory is used as a frame memory, the hardware window function cannot be used, or even if it can be, the number of additional circuits is increased.